Oil seeds and especially soy beans are often processed in the foodstuff industry, thereby grinding them in dry condition by means of hammer mills or disintegrators, or by treating them in an extruder. The particle sizes thus obtained are relative coarse, the cell membranes are practically not opened or disintegrated, and a fine powder, as is necessary to produce soy milk and soy milk products, cannot be obtained.
In order to produce soy milk, generally colloid mills are used (vide e.g. U.S. Pat. No. 3,399,997, column 2, lines 59 ff), whereby grinding is effected in wet condition of the soy beans. From the suspension obtained, either drinkable soy milk is produced or the soy milk is coagulated to produce the so-called "tofu"-cheese. In such a wet processing, the protein contained in the soy beans (or similar oil seeds) become dissolved, whereas the cell walls have to be filtered or pressed off. In doing so, a relative high loss of protein will result, amounting up to 50% percent. A further disadvantage of the known wet-grinding method resides in that the combination of starch and proteins contained in the oil seeds leads to a considerable viscosity resulting in a high power consumption of the colloid mills on the one hand, and to the need to dry the product on the other hand, if only the powder should be obtained and not a milk.
In fact, attempts have also been made to extract the protein contained in soy beans by a chemical means. In order to obtain a better effect of the extraction solvent, in this connection it has been proposed to grind the soy beans in dry condition (e.g. U.S. Pat. Nos. 2,802,738, 3,288,614 or 3,645,745). Just because a mechanical extraction of the protein could not be obtained by the methods used heretofore, a subsequent chemical treatment was required. Such processes have also been proposed for debittering soy beans, but such chemical processes are not always in accordance with the governmental rules concerning foodstuffs.